In arranging evacuation plants or systems for the evacuation of leaked out or otherwise free anesthesia or analgesia gases it is naturally very important to design and dimension the suction devices in an appropriate way. At the same time it is urgent and important to adjust the capacity of the suction sources in such a way that the suction force remains at the desired value. The Swedish patent No 8008962-6 and European patent No. EP 0 067 196 disclose a known anesthesia mask, equipped with means for evacuation of leaked out gas and the mask is so designed that it catches or collects and evacuates gas leaking out between the mask edge and the face of the patient, but is also so arranged that it is able to catch and evacuate all gas streaming out from the mask as the mask is removed from the face of the patient and is held free. For this purpose the mask proper is equipped with a circumferential slot or opening connected to a suction source. Behind the invention lies a number of problem which now have found a solution, viz.
evacuation also of gases exhaled by the patient PA1 noise generation at the device PA1 adaption of the capacity to different sizes of anesthesia masks.
With modern anesthesia arrangements there are besides the means for supplying of anesthesia gas also an evacuation system, which is adapted to remove the exhaled gas mixed with air directly from the mask. Thus, to the mask there are connected both a gas supply main and an evacuation main and furthermore the suction pipe or tube connected to the slot evacuation arrangement of the mask according to the above patents. It is of utmost importance that the vacuum inside the evacuation main is maintained at such a level that the respiratory system of the patient in no way will be affected and this is the reason why there are built in safety devices preventing the vacuum from adversely affecting the patient. The capacity of the evacuation system is normally of a range 20-30 liters per hour. With systems of the type described and including so called double mask devices principally no gas at all or very little gas will leak out in the operation theater.
A known apparatus discloses a control valve having a input opening for so called fresh gas, i.e. the intended mixture of anesthesia gas and oxygen/air and to this input opening a compensation ballon is connected to an open branch pipe, which ballon in sequence with the breathing of the patient will be emptied and filled again. The evacuation line for exhaled air is also arranged at the control valve and via an open branch line connected with a so called reservoir, i.e. a flexible tank or container open towards the atmoshpere, also serving as a balancing or compensation means but having as its main purpose to prevent a vacuum build up beyond the allowed limits in the evacuation main if the pipe or tube to the mask would be partially blocked.
Many hospitals and clinics, however, have no permanent systems for the supply of anesthesia gas and the evacuation of exhaled air, but utilize portable anesthesia apparatuses and gas bottles. With such apparatuses the exhalation normally is done directly into the operation theatre via a check valve arranged at the mask, which naturally results in a severe contamination of the air in the operating theatre and necessiatates a powerful general ventilation thereof. The use of masks of the type mentioned earlier herein and securing an evacuation of leaked out gas along the edge of the mask and capturing gas from the mask when lifted, naturally partially improves the situation, but is in no way sufficient as the exhaled air with its high anesthesia gas contents escapes freely into the operation theatre atmosphere.
Even if systems and plants arranged for the use of so called double masks work highly satisfactorily both technically and functionally there is an irritating thing which is regarded as disturbing, viz. the sound, or rather noise, generated by the evacuation. There even exist a certain, although small, risk in that the staff--in order to get rid of the noise--under certain circumstances will reduce the suction capacity alternatively and turn off the apparatus alltogether.
Another possible point of irritation is the cooling effect occuring when an airstream passes the hands, for example, of a person staying close to the place of evacuation and also the cooling effect occuring when holding a hose or a pipe, through which air or gas streams. It is furthermore desirable to keep both free gas and air streams and streams inside pipes and tubes at the lowest possible velocity level.
Decisive for a proper function of the system according to the European and Swedish patents is, as already mentioned, the ability of suction, but for the overall performance not only the suction ability is of importance. If that were the case one could restrict the system to just as large a ventilator or fan device as possible.
The suction ability may be too low. Then it is unable to attract the streams of gas which just pass by. The suction ability also can be to powerful, and bias the intended flow of anesthesia gases and in difficult cases also have an inpact on the respiration of the patient. To this may be added the cooling effect created when an air stream passes the facial skin or the like and such draft caused by the suction means is highly unpleasant when felt. The velocity or volume of the sucked in air also is of significance with regard to the sound generation. On low velocity the sound will be hardly noticeable, but as soon as the velocity increases, the sound will increase.
The volume of supplied fresh gas and volume of exhaled air respectively naturally vary with the the patients. A small child does not need as large a volume of fresh gas and does not exhale as large volumes as a grown person. It would be desirable to not only supply fresh gas to but also evacuate and remove gas from the patient in question in the same way as different types and sizes of masks are used depending on the patient.